package cn.bellychang.ood.litejunit.v3.framework;

/**
 * @author ChangLiang
 * @date 2020/5/27
 */
public class ComparisonFailure extends Throwable {
    private static final int MAX_CONTEXT_LENGTH= 20;
    private static final long serialVersionUID= 1L;

    private String fExpected;
    private String fActual;

    /**
     * Constructs a comparison failure.
     * @param message the identifying message or null
     * @param expected the expected string value
     * @param actual the actual string value
     */
    public ComparisonFailure (String message, String expected, String actual) {
        fExpected= expected;
        fActual= actual;
    }

    /**
     * Returns "..." in place of common prefix and "..." in
     * place of common suffix between expected and actual.
     *
     * @see java.lang.Throwable#getMessage()
     */
    public String getMessage() {
        return new ComparisonCompactor(MAX_CONTEXT_LENGTH, fExpected, fActual).compact(super.getMessage());
    }

    /**
     * Returns the actual value
     * @return the actual string value
     */
    public String getActual() {
        return fActual;
    }
    /**
     * Returns the expected value
     * @return the expected string value
     */
    public String getExpected() {
        return fExpected;
    }

    private static class ComparisonCompactor {
        private static final String ELLIPSIS= "...";
        private static final String DELTA_END= "]";
        private static final String DELTA_START= "[";

        private int fContextLength;
        private String fExpected;
        private String fActual;
        private int fPrefix;
        private int fSuffix;

        public ComparisonCompactor(int contextLength, String expected, String actual) {
            fContextLength= contextLength;
            fExpected= expected;
            fActual= actual;
        }

        public String compact(String message) {
            if (fExpected == null || fActual == null || areStringsEqual())
                return Assert.format(message, fExpected, fActual);

            findCommonPrefix();
            findCommonSuffix();
            String expected= compactString(fExpected);
            String actual= compactString(fActual);
            return Assert.format(message, expected, actual);
        }

        private String compactString(String source) {
            String result= DELTA_START + source.substring(fPrefix, source.length() - fSuffix + 1) + DELTA_END;
            if (fPrefix > 0)
                result= computeCommonPrefix() + result;
            if (fSuffix > 0)
                result= result + computeCommonSuffix();
            return result;
        }

        private void findCommonPrefix() {
            fPrefix= 0;
            int end= Math.min(fExpected.length(), fActual.length());
            for (; fPrefix < end; fPrefix++) {
                if (fExpected.charAt(fPrefix) != fActual.charAt(fPrefix))
                    break;
            }
        }

        private void findCommonSuffix() {
            int expectedSuffix= fExpected.length() - 1;
            int actualSuffix= fActual.length() - 1;
            for (; actualSuffix >= fPrefix && expectedSuffix >= fPrefix; actualSuffix--, expectedSuffix--) {
                if (fExpected.charAt(expectedSuffix) != fActual.charAt(actualSuffix))
                    break;
            }
            fSuffix=  fExpected.length() - expectedSuffix;
        }

        private String computeCommonPrefix() {
            return (fPrefix > fContextLength ? ELLIPSIS : "") + fExpected.substring(Math.max(0, fPrefix - fContextLength), fPrefix);
        }

        private String computeCommonSuffix() {
            int end= Math.min(fExpected.length() - fSuffix + 1 + fContextLength, fExpected.length());
            return fExpected.substring(fExpected.length() - fSuffix + 1, end) + (fExpected.length() - fSuffix + 1 < fExpected.length() - fContextLength ? ELLIPSIS : "");
        }

        private boolean areStringsEqual() {
            return fExpected.equals(fActual);
        }
    }
}
